There are various techniques of noninvasively measuring the inside of the living body. Optical measurement, as one of such techniques, has merits of being free from the problem of exposure to radiation and capable of selecting a compound as a measurement target by selecting a wavelength. A general biometrical measurement apparatus is designed to emit the inside of the living body with light while a light emission unit is pressed against the surface of the skin of the living body and to measure transmitted or reflected light which is transmitted through the skin again and emerges out of the living body and calculate various types of biometrical information based on the measurements. The presence of an abnormal tissue in the living body is determined by optical measurement based on the difference in light absorption coefficient between the abnormal tissue and a normal tissue. That is, the difference in absorption coefficient between normal and abnormal tissues in the living body leads to a difference in the amount of light detected based on a difference in the amount of light absorbed. Therefore, solving an inverse problem from the amount of light detected can obtain the absorption coefficient of an abnormal tissue. A characteristic of the abnormal tissue can be discriminated from the obtained absorption coefficient. In addition, the measurement position and depth are analyzed from the measured light. Such analysis techniques include a technique (spatial decomposition method) of adjusting the distance between a light emission unit (or light source) and a detector, a technique (time decomposition method) of obtaining depth information from a difference in the arrival time of light by using a light source whose intensity changes with time, and a method as a combination of them. These analysis methods implement a biometrical measurement apparatus which can acquire high-quality signals. However, the technique of imaging information based on light in the living body has the problem of a low spatial resolution. In addition, in order to obtain correct position information from the result of detecting reflected light, it is necessary to compute many data using a complicated algorithm. This makes it impossible to perform real-time determination.
Highly feasible applications of optical biometrical measurement include breast cancer examination. As described above, however, since performing optical measurement alone leads to problems in terms of resolution and analysis time, it is preferable to improve examination performance by using this technique in combination of another modality. For this reason, the present inventors have proposed a scheme of compensating for the low spatial resolution of light by using the morphological information of ultrasonic echoes. Although this scheme is expected to be capable of discriminating morphological characteristics in living body tissues and the partial distribution of morphological characteristic portions within a shorter time than in a related art, there is still room for improvement in immediate determination.
Breast cancer is one of the causes of women death. Breast cancer screening and early diagnosis have very high values in terms of reducing mortality rate and suppressing the cost of health care.
Existing methods include palpation of breast tissues and X-ray imaging for searching for suspected tissue deformation. If there is a suspected portion in an X-ray photograph, ultrasonic imaging is performed, and surgical tissue examination is further performed. A series of these examinations require much time to reach a final conclusion. In addition, since premenopausal young women have many mammary glands, high sensitivity is difficult to obtain in X-ray imaging. Therefore, screening using ultrasonic imaging has great significance for the young generation, in particular.
In general, in ultrasonic imaging, a certified operator acquires ultrasonic still images, and an expert interpreter (a plurality of interpreters in some cases) makes determination from morphological information on the images. When performing medical examination, the maximum number of persons subjected to screening per operator per day is 50 in consideration of the risk of oversights caused by the fatigue and lack of concentration of the operator.
In order to acquire a still image capturing a morphological characteristic in ultrasonic imaging, it is very important for the operator to have knowledge and experience. High skill is also required to perform accurate and quick screening. For example, standard examination times per object are 5 to 10 min. However, it sometimes takes more time for screening depending on the skill of an operator. That is, in screening based on current ultrasonic imaging, the accuracy of image acquisition may vary depending on the levels of skill of operators. When acquiring images, the operator needs to keep paying close attention to images. Besides, he/she takes charge of making determination by himself/herself, and hence a heavy metal strain is imposed on him/her even if he/she is a skilled operator. Although there is available a scheme of acquiring all image information from a moving image, there is no established technique for mechanical search using image recognition. For this reason, an interpreter searches a moving image for still images. In this case, a heavy burden is imposed on the interpreter.
In order to solve the above problem, the present applicant has proposed an apparatus with the concept of complement of ultrasonic echo diagnosis by using a compact optical examination system designed to reduce a burden on a technician by guiding the measurement position of an ultrasonic echo probe in a plane direction based on the metabolic information of the living body which is obtained by optical measurement. FIG. 18 shows the light absorption spectra of oxygenated hemoglobin and deoxygenated hemoglobin. In general, deoxygenated hemoglobin in a malignant tumor region is higher in ratio than in a healthy region, and hence an analysis result on the absorption of deoxygenated hemoglobin is one of the bases for determining the degree malignancy of a target region in optical biometrical examination. The wavelength regions of light suitable for the light absorption measurement of deoxygenated hemoglobin are 740 nm to 790 nm in the near-infrared light region and 650 nm to 690 nm in the red light region. The wavelength region of light suitable for the light absorption measurement of oxygenated hemoglobin is 830 nm to 900 nm in the near-infrared light region. The wavelength region of light to identify a total hemoglobin amount is, for example, 800 nm to 820 nm in the near-infrared light region. Specific light sources include an LED and an LD. In consideration of absorption wavelength of other biological components such as water, fat, and melanin and biodistributions, an output light intensity and a half width must be properly selected for a light source.
One of the problems in conventionally proposed biometrical measurement apparatuses is that a measurement target to which an ultrasonic echo probe is guided by an optical measurement system is not always located immediately below the probe. This problem originates from the selection of an arrangement in which the longitudinal symmetrical axis of the ultrasonic echo piezoelectric probe is orthogonal to a symmetrical axis of the optical measurement system.
In order to solve this problem, the present inventors have proposed the arrangement of a probe configured such that a symmetrical axis of an optical measurement system substantially coincides with the longitudinal axis of an ultrasonic echo piezoelectric probe (a symmetrical axis of an optical measurement system is arranged to be parallel to the longitudinal direction of the piezoelectric probe and fall within its short side). In such a typical probe arrangement, a light introducing unit is arranged at a position near a short side of the piezoelectric probe, and a plurality of detection units are symmetrically arranged near a probe short side. This avoids the problem that a measurement target is positioned outside the piezoelectric probe.
In this arrangement, however, since a measurement target is positioned at an end of an echo image, it is not possible to meet the need to guide a target to the central position to perform examination while rotating the probe. In order to solve this problem, the present inventors have selected an arrangement in which a plurality of light sources are arranged near the central position of the piezoelectric probe so as to be symmetrical with respect to an axis in the long-side direction, and a plurality of detection units to be paired with the light sources are arranged symmetrically with respect to the axis in the short-side direction of the piezoelectric probe. This arrangement makes it possible to guide a measurement target to the central position of an echo probe. In addition, the present inventors have also proposed an optical detection system which has been improved in terms of the implementation of a multiple light source scheme in order to solve the problem that the amount of light absorbed changes because the probe is brought into pressure contact with the skin.
This probe arrangement is suited to guide an abnormal region to a position immediately below the middle of the probe, but can only roughly estimate the depth and size of a region. For this reason, when, for example, it is necessary to perform image examination with a spatial resolution of 5 mm, data obtained by one measurement is not enough for the examination. Obviously, the problem can be solved by greatly increasing the numbers of light incident positions and detection positions. This requires an enormous calculation amount and an enormous calculation time. In addition, as the number of channels increases accordingly, the detection system increases in size. This makes it impossible to meet the need for a compact system which complements ultrasonic echoes.
To solve this problem, imaging can be implemented by acquiring the necessary number of data by performing a plurality of measurements with an arrangement whose relative position is properly changed. However, it is highly difficult to perform accurate positioning in biometrical examination. In addition, when the surface of the living body is scanned with a probe, the distribution of blood changes by the pressure on the skin. For this reason, bringing the probe into contact with the skin with a high repeatability also increases the difficulty in measurement. As described above, examination technicians are required to have high skills and techniques.
In order to solve the above problems, this embodiment has as its object to provide an ultrasonic diagnostic apparatus and a biometrical examination apparatus which can increase the amount of measurement data while easily and accurately measuring the relative position of an ultrasonic probe at the time of biometrical measurement when guiding the position of the probe.